1. Bacteriophages (phages) are viruses that infect bacterial cells. One application of them is to infect the bacteria on food to kill them so they do not cause human disease. Bacteriophages do not infect human cells.

2. One useful technique for purifying recombinant proteins from cells is called histidine tagging. In this method, the recombinant gene is inserted in a plasmid such that a string of 6 histidine amino acids is linked to the amino end of the recombinant protein. The histidines will bind to a nickel ion on a column. To purify the desired protein, the mixture of proteins from the cell is passed throught he column. Only the recombinant protein will bind to the nickel because it is the only one with the 6 histidines at the end. All other proteins will then pass through the column, leaving the recombinant in a pure form.

3. Genomic libraries allow researchers to collect all of the genomic DNA of an organism in thousands of E. coli cells. These are made by cleaving genomic DNA with a restriction enzyme and then cleaving a plasmid with the same enzyme. All of the genomic fragments are ligated into plasmids (one piece per plasmid). The plasmids are transformed into bacteria and the colonies that grow (in sum) contain all of the original organisms DNA - one piece per each colony. These can be screened and desired genes from the original organism can be isolated from colonies.

4. Reverse transcriptase is a DNA polymerase from retroviruses (like HIV) that can make DNA using RNA as a template. It is used in biotechnology to convert mRNA to DNA (making a cDNA)so it can be inserted into a plasmid. Using this technology, one can isolate all of the mRNAs of a cell, make cDNA, and then make a cDNA library similar to the genomic library above.

5. The Polymerase Chain Reaction (PCR) was invented in the late 1980s. It provides a way to amplify DNA sequences (make more of them) starting with very tiny amounts of a target DNA. The process borrows from the mechanism of DNA replication. It requires a target DNA, two primers (one for each strand), 4 dNTPs, and a DNA polymerase (such as Taq DNA Polymerase) that is resistant to denaturation under high temperatures. A cycle of PCR consists of priming the DNA strands, DNA replication, and denaturation. Each cycle of PCR can double the amount of DNA present. After 30 cycles, a theoretical amplification of over 1 billion fold is theoretically possible.

6. DNA fingerprinting is a technique (that uses PCR) that allows one to determine the linkage between a DNA a person. It relies on the fact that some regions of the human genome differ more than others. By amplifying these regions of DNA and analyzing their differences in size of fragments, one can determine with reasonable certainty if a DNA sample matches a person's DNA.

Highlights Viruses

1. Viruses infects cells of all types.

2. Viruses contain nucleic acid (RNA or DNA, single-stranded or double-stranded, depending on the virus) and have a protein coat.

3. The protein coat comes from a gene encoded by the virus and it allows the virus to attach to the cell(s) it infects.

4. Viral infection includes the steps of 1) attachment; 2) injection of the viral nucleic acid; 3) replication and translation of the viral information by the cell; 4) packaging of the viral nucleic acid into coat proteins; and 5) bursting of the cell to release viral particles for more infection.

5. HIV is a retrovirus, meaning it has an RNA genome and an enzyme called reverse transcriptase that converts the viral RNA into double-stranded DNA. HIV has a protein that attaches to CD-4 (a protein found on the membrane of immune system cells)

6. When double stranded viral HIV DNA is made, an enzyme called integrase inserts (attaches) it inside of the host chromosome where it stays. The inserted DNA has a strong promoter that RNA polymerase uses to make more copies of the viral RNA, which continues the cycle.